This invention is directed to organic electroluminescent (EL) devices, and more specifically, to organic EL devices with a number of excellent performance characteristics inclusive of the enablement of blue emitting EL devices, which devices contain luminescent components or a luminescent component with excellent high thermal stability, film forming characteristics and intense blue fluorescence. Organic EL devices are desired that are capable of providing uniform luminescence, saturated color especially in the blue regions of the visible spectrum, and low driving voltages. The organic EL devices of the present invention enable in embodiments the above characteristics and which devices contain organic luminescent materials or light emitting components comprised of fluorescent hydrocarbon compounds, and which devices can be selected for use in flat-panel emissive display technologies, including TV screens, computer screens, and the like.
A simple organic EL device can be comprised of a layer of an organic luminescent material conductively sandwiched between an anode, typically comprised of a transparent conductor, such as indium tin oxide, and a cathode, typically a low work function metal such as magnesium, calcium, aluminum, or the alloys thereof with other metals. The EL device functions on the principle that under an electric field, positive charges (holes) and negative charges (electrons) are respectively injected from the anode and cathode into the luminescent layer and undergo recombination to form excitonic states which subsequently emit light. A number of prior art organic EL devices have been prepared from a laminate of an organic luminescent material and electrodes of opposite polarity, which devices include a single crystal material, such as single crystal anthracene, as the luminescent substance as described, for example, in U.S. Pat. No. 3,530,325. However, these devices usually require excitation voltages on the order of 100 volts or greater.
In U.S. Pat. No. 4,539,507 there is disclosed an EL device formed of a conductive glass transparent anode, a hole transporting layer of 1,1-bis(4-p-tolylaminophenyl)cyclohexane, an electron transporting layer of 4,4xe2x80x2-bis(5,7-di-tert-pentyl-2-benzoxzolyl)stilben, and an indium cathode.
U.S. Pat. No. 4,720,432 discloses an organic EL device comprising a dual-layer hole injecting and transporting zone, one layer being comprised of porphyrinic compounds supporting hole injection and the other layer being comprised of aromatic tertiary amine compounds supporting hole transport.
U.S. Pat. No. 4,769,292 discloses an EL device employing a luminescent zone comprised of an organic host material capable of sustaining hole-electron recombination and a fluorescent dye material capable of emitting light in response to energy released by hole-electron recombination. A preferred host material is an aluminum complex of 8-hydroxyquinoline, namely tris(8-hydroxyquinolinate)aluminum.
While recent progress in organic EL research has elevated the potential of organic EL devices for widespread applications, the performance levels of a number of current available devices, especially with respect to blue emission, may still be below expectations. Further, for visual display applications, organic luminescent materials should provide a satisfactory color in the visible spectrum, normally with emission maxima at about 460, 550 and 630 nanometers for blue, green and red. These organic EL devices may comprise a light-emitting layer which is comprised of a host material doped with a guest fluorescent material that is responsible for color emission. For efficient down-shifting of EL emission wavelength in the host-guest emitting layer, it may be desirable that the host material should fluorescence in the blue or shorter wavelength region. In many conventional organic EL devices, the luminescent zone or layer is formed of a green-emitting luminophor of tris(8-hydroxyquinolinate)aluminum with certain fluorescent materials. U.S. Pat. No. 5,409,783 discloses a red-emitting organic EL device by doping the tris(8-hydroxyquinolinate)aluminum layer with a red fluorescent dye. However, up-shifting of the tris(8-hydroxyquinolinate)aluminum emission to blue region is believed to be highly inefficient. Although there have been several disclosures describing blue-emitting organic EL devices, for example in U.S. Pat. Nos. 5,151,629 and 5,516,577, the disclosures of which are totally incorporated herein by reference, their performance characteristics still possess many disadvantages such as poor emission hue, high operation voltages, low luminance, and poor operation stability. Thus, there continues to be a need for improved luminescent compositions for organic EL devices, which may vacuum evaporable and form thin films with excellent thermal stability. There is also a need for luminescent compositions which are capable of providing uniform and satisfactory emission in the blue region of the light spectrum. In particular, there is a need for efficient blue luminescent materials for organic EL devices, which may optionally be doped with a fluorescent dye. Further, there is also a need for luminescent compositions which can enhance charge transporting characteristics, thus lowering device driving voltages. Therefore, a primary feature of the present invention is to provide luminescent materials comprised of certain fluorescent hydrocarbon compounds, which in comparison to certain EL devices comprised of the metal chelates of oxadiazole compounds can provide improved and excellent emission characteristics particularly in the blue region, such as a saturated blue color and a narrow emission spectrum.
It is a feature of the present invention to provide luminescent compositions for organic EL devices.
It is another feature of the present invention to provide organic EL devices with many advantages, such as low operation voltages, uniform light emission with spectrum spreading from blue to longer wavelengths, thermal stability, electrochemical stability, and charge transport capability.
In an another feature of the present invention there are provided organic EL devices with a light emitting layer containing a luminescent material comprised of novel fluorescent hydrocarbon compounds.
In yet another feature of the present invention there are provided organic EL devices with a light-emitting layer comprised of a luminescent hydrocarbon compound.
Further, in a feature of the present invention there are provided organic EL devices comprised of a supporting substrate of, for example, glass, an anode, an optional buffer layer, a vacuum deposited organic hole transporting layer comprised of, for example, 4,4xe2x80x2-bis-(9-carbazolyl)-1,1-biphenyl, a vacuum deposited light emitting layer comprised of a luminescent hydrocarbon compound, an optional vacuum deposited electron transporting layer, and in contact therewith a low work function metal, such as magnesium, lithium, and their alloys as a cathode.
Yet in another feature of the present invention there is provided an organic EL device comprised of a supporting substrate of, for example, glass, an anode, an optional buffer layer, a vacuum deposited organic hole transporting layer comprised of tertiary aromatic amines, for example, N,Nxe2x80x2-1-naphthyl-N,Nxe2x80x2-diphenyl-1,1xe2x80x2-biphenyl-4,4xe2x80x2-diamine, a vacuum deposited light emitting layer, an optional vacuum deposited electron transporting layer, and in contact therewith a low work function metal, such as magnesium and its alloys as a cathode, wherein the light emitting layer is comprised of a mixture of a novel hydrocarbon compound as a host component and an optional fluorescent material.
These and the other features of the present invention are accomplished by the provision of luminescent or light emitting components comprised of the hydrocarbon compounds illustrated by the Formula (I) 
wherein R1 and R2 are substituents, which may be selected from the group consisting of hydrogen, an alkyl group with, for example, from 1 to about 25, and more specifically, to about 6 carbon atoms, an aryl group with about 6 to about 30 carbon atoms, an alkoxy group with from 1 to about 25, and more specifically, to about 6 carbon atoms, a halogen, a cyano group and the like; Ar1 and Ar2 are each an aromatic component, such as an aryl group with, for example, about 4 to about 10 conjugate-bonded or fused benzene rings, and which may be independently selected, for example, from the group consisting of those as represented by or encompassed by the following formulas 
wherein R11, R12, R13, R14, and R15 are each a substituent selected from the group consisting of hydrogen, an alkyl group with, for example, from 1 to about 6 carbon atoms, an alicyclic alkyl group with from about 3 to about 15 carbon atoms, an alkoxy group with, for example, preferably from 1 to about 6 carbon atoms, a dialkylamino group with preferably from about 1 to about 3 carbon atoms, a halogen, a cyano group and the like.
The features of the present invention can be also accomplished by the provision of luminescent or light emitting components comprised of the hydrocarbon compounds illustrated by Formula (II) 
wherein R1 and R2 are substituents, which may be selected from the group consisting of hydrogen, an alkyl group with, for example, preferably from 1 to about 6 carbon atoms, an alicyclic alkyl group with from about 3 to about 15 carbon atoms, an aryl group with about 6 to about 30 carbon atoms, an alkoxy group with preferably from 1 to about 6 carbon atoms, a halogen, a cyano group and the like; R3, R4, R5, and R6 are each a substituent, which may be selected from the group consisting of hydrogen, an alkyl group with, for example, preferably from 1 to about 6 carbon atoms, an alicyclic alkyl group with from about 3 to about 15 carbon atoms, an aryl group with about 6 to about 30 carbon atoms, an alkoxy group with preferably from 1 to about 6 carbon atoms, and the like, wherein R3 and R4, or R4 and R5 may optionally be combined into a bivalent hydrocarbon group, and is, for example, selected from the group consisting of an alkylene group with from about 3 to about 8 carbon atoms, an alkylidene group with from about 3 to about 15 carbon atoms, an alicyclic alkylidene group with from about 3 to about 15 carbon atoms, and a arylalkylidene group with from about 6 to about 30 carbon atoms, and the like; Ar1 and Ar2 are each an aromatic component, such as an aryl group with from about 6 to about 30 carbon atoms, or an arylvinyl group with from about 6 to about 30 carbon atoms, which may, for example, be selected from the group consisting of a phenyl, a biphenylyl, a 3,5-diarylphenyl, a phenylvinyl, a diphenylvinyl, and the like; and wherein Ar is a tetravalent aromatic group with, for example, from about 6 to about 60 carbon atoms, and which group may selected, for example, from the group consisting of the following formulas 
wherein R11, R12, and R13 are each a substituent, which may be selected from the group consisting of hydrogen, an alkyl group with, for example, preferably from 1 to about 6 carbon atoms, an alicyclic alkyl group with from about 3 to about 15 carbon atoms, an alkoxy group with, for example, preferably from 1 to about 6 carbon atoms, a dialkylamino group with preferably from about 1 to about 3 carbon atoms, a halogen, a cyano group and the like.
In embodiments, the present invention relates to organic EL devices that are comprised in the following order of a supporting substrate of, for example, glass, an anode, an optional buffer layer, an organic hole transporting layer, an organic light emitting hydrocarbon layer, and an optional electron transporting layer, and in contact therewith a low work function metal as a cathode, wherein the light emitting layer contains at least one luminescent hydrocarbon compound illustrated and encompassed by the formulas recited herein, for example (I) and (II); and layered EL devices with a light emitting layer comprised of a luminescent composition comprised of a hydrocarbon compound illustrated by, for example, Formulas (I) and (II) as a host component capable of sustaining hole-electron recombination and a guest fluorescent material capable of emitting light in response to energy released by the hole-electron recombination. The light emitting layer may be formed by vacuum deposition from evaporation of the fluorescent hydrocarbon material, and wherein the presence of the fluorescent material permits a wide latitude of wavelengths of light emission and may enable the enhancement of electroluminescent efficiency and improvements in device operation stability.
The luminescent or light emitting hydrocarbon materials illustrated herein possess in embodiments several advantages. For example, the hydrocarbon compounds exhibit strong fluorescence in the solid state in the region of from about 400 nanometers to longer wavelengths of, for example, about 600 nanometers; they have the ability of forming thin films with excellent thermal stability by vacuum evaporation; they are stable; and they can also be blended with a number of fluorescent materials to form a common phase.
The FIGURE illustrates an EL device or an organic light emitting diode which is comprised of a supporting substrate 1 of, for example, glass; an anode 2 of, for example, indium tin oxide in a thickness of from about 1 to about 100 nanometers and preferably from about 10 to about 80 nanometers (throughout the thickness ranges for each layer are examples and other suitable thickness may be selected); optionally a buffer layer 3 of, for example, copper (II) phthalocyanine in a thickness of from about 5 to about 80 nanometers and preferably from about 10 to about 40 nanometers; an organic hole transporting layer 4 of an aromatic amine compound, for example N,Nxe2x80x2-1-naphthyl-N,Nxe2x80x2-diphenyl-1,1xe2x80x2-biphenyl4,4xe2x80x2-diamine in a thickness of from about 1 to about 100 nanometers and preferably from about 5 to about 80 nanometers; an organic light emitting layer 5 comprised of a luminescent hydrocarbon compound of the formulas or encompassed by the formulas illustrated herein in a thickness of from about 1 to about 100 nanometers and preferably from about 20 to about 80 nanometers; an organic electron transporting layer or hole blocking layer 6 of, for example, 4,4xe2x80x2-bis-[2-(4,6-diphenyl-1,3,5-triazinyl)]-1,1xe2x80x2-biphenyl or tris-(8-hydroxyquinolinato)aluminum in a thickness of from about 1 to about 300 nanometers and preferably from about 10 to about 80 nanometers, and in contact therewith a low work function metal as a cathode 7. In this EL device, a junction is formed between the hole transporting layer and the light emitting layer. In operation, when the anode is electrically biased to a positive potential with respect to the cathode, holes are injected into the organic hole transporting layer and transported across this layer to the junction. Concurrently, electrons are injected from the cathode to the electron transport layer and are transported toward the same junction. Recombination of holes and electron occurs near the junction resulting in light emission. Optionally, the light emitting layer can contain more than one luminescent hydrocarbon compound illustrated and encompassed by the Formulas recited herein, for example (I) and (II); and layered EL devices with a light emitting layer comprised of a luminescent composition comprised of a hydrocarbon compound illustrated by, for example, Formulas (I) and (II) as a host component capable of sustaining hole-electron recombination and a guest fluorescent material capable of emitting light in response to energy released by the hole-electron recombination.